(1) Field of the Invention
This invention pertains to devices for the control and synchronization of automobile traffic signals. More particularly, this invention pertains to synchronization devices which use the cycles of the alternating current power source, nominally 60 hz, as a common time reference to maintain the operating cycles of a series of traffic signals in synchronization and to maintain fixed time delays between the various traffic signals to coordinate the traffic flow.
(2) Description of the Prior Art
Synchronization devices in the prior art use a digital counter to count the cycles of the alternating current power source to provide a common time reference. When the counter reaches a number corresponding to the length of the traffic light operating cycle the counter re-sets to zero and starts counting again. In the prior art the cycle counters in all of the synchronized traffic control devices are re-set once a day to zero by a system wide, time of day, re-synchronization pulse. Offsets or time-delays between the operating cycles of individual traffic signals are obtained by generating a synchronizing pulse from the cycle counter whenever the cycle counter reaches an intermediate count corresponding to the desired offset or time-delay for the particular traffic signal. This synchronization pulse, in turn, initiates and times the operating cycle of the individual traffic signal.
A problem arises in the operation of the prior art device whenever the length of the operating cycle of the traffic light is altered. After the cycle length in each light is altered, each cycle counter in the traffic control system must wait for the next daily re-synchronization pulse before the system is again synchronized.